The problem is: if you have a character who is dead and you want to let us know that he is dead by constantly bathing him in blue light, how do you do it when there are three or four or six or eight other characters onstage bathed in such bright white light that blue won't show up against the white at all? Or, to put the problem in reverse, if you want to lower the stage lights to the point where a dull blue dominates the semi-darkness, how do you keep the other characters from tripping over the furniture?I don't really want to be flippant about the difficulties that literally haunt Lanford Wilson's latest addition to the Talley saga, ''A Tale Told'' at the Circle Rep in Sheridan Square, because Mr. Wilson is a writer of considerable talent and because I so liked the simplest of his three plays about a Missouri household, ''Talley's Folly.'' But the new piece - I am told that there may be five of them before the entire chronicle can be called completed - is so patently unsure of itself as it gropes for a shape that The Puzzle of the Blue Light becomes a symbol of its rather wistful waywardness.Beginning this way. As members of the Talley clan are opening up and airing out the long unused ''front parlor'' of the house on the very same night (July 4, 1944) that the Sally of ''Talley's Folly'' is meeting her Jewish suitor down by the boathouse, one of the figures winding in and about the busy group is utterly silent. He is also dressed in the camoflage fatigues of World War II. After a brief moment of being ignored by the clucking women who are tidying up beneath the buttercup-shaped globes of the chandelier, he slips to the French windows, smiles at the others gently, and disappears into the garden. Though there has been no blue light yet - at least none that we can notice - we can guess this illusive G.I. is a younger son of the household and that he is very probably dead. We have seen plays like ''Sticks and Bones'' and are pretty quick about these things now.Inasmuch as he does not return for quite a while, we are compelled to devote our attention to the living, though without sufficient introduction. Among the six or more people flitting or sitting about there are two we can nail down without undue effort: Lottie, an owlish member of the group with a pleasantly tart tongue who is nonetheless in severe pain from radium poisoning; and a neighboring laundress who seems to have modeled her performance on Thelma Ritter. It takes us an unconscionable time, however, to sort out the balance of the company - five more will be coming along soon - and I began to wonder if Mr.Wilson wouldn't have been better off stealing a device from ''Talley's Folly.'' In that charming piece, you'll remember, he let his ardent interloper, Matt, initiate the festivities by chatting candidly with the audience, explaining something of what was going on. Mightn't he, I asked myself, have used his spectral soldier, now merely lurking in the wings, to similar purpose, letting him tick off his relations for us as they scurried onto the stage and offering us a few quick clues to their temperaments? A scorecard, sort of. (I later decided that this was not a very good idea, after all. Once our in-and-out ghost did begin to speak, in lengthy soliloquies detailing his battle experiences, he proved wearingly irrelevant to the needs of this particular play.)In any event, and after some tortured exposition, we do learn a bit more. We grasp that the Talley patriarch, expertly played by the leonine Fritz Weaver, may or may not be senile; but whatever he is, and however rapidly he may have to be rushed to the bathroom, he still rules the roost. We grasp that his son, in the subdued and oddly likeable performance of Michael Higgins, is unaggressive in business matters; on the other hand, he seems to have sired the 17-year-old blond daughter of the laundress. And we grasp that a conglomerate wishes to take over the Talley factories, which are at present very busy making uniforms. Mr. Higgins is against selling, for fear the product will be cheapened. Mr. Weaver and a factory manager, played with finesse and a false shyness by Jimmie Ray Weeks, lean toward a deal. The Talley place, as in ''The Fifth of July,'' is in constant danger of being sold off.Now, our slippery young soldier has been reappearing along the way, though thus far only when the parlor is temporarily empty. The absence of other actors, you see, permits the stage lights to dim and go blue without any special explanation. A stylistic formality, and no questions asked. But. A moment comes when matters of stylistic formality are shot right to hell. Pretty rudely, too, in my opinion.It so happens that among those visiting the old homestead just now is a second soldier son, a live one, whose name is Buddy. And it also so happens that Buddy has a wife, a decided fussbudget. Buddy's wife, if I remember correctly, has been heard to remark, early on, that during wartime it's a fine thing to save electricity. Whatever her remarks may have been, there arrives a time when an important conference is going on among a number of Talleys and Talley associates in the living room. Without so much as a by-your-leave, Buddy's wife marches straight into the assembly and begins putting out every light in the place. She has to do it one by one, so it takes her some time, but she is resolute. The room is also becoming darker, a fact gradually noticed by the conferees. Rather than risk their necks falling over ottomans in the enveloping gloom, they promptly get out of there, presumably to continue the play in the kitchen. Question. Is Buddy's wife all that determined to save electricity? No, of course she's not. She's paving the way for that ectoplasmic youngster to come on again, and we know it. He does come on. So do the blue spotlights overhead. When his monologue is at last done, someone - Mr. Higgins, I think - must enter and snap on all the switches again, a chore performed with the most salutary patience.The entire episode seems to me the most useless and ostentatiously awkward attempt to justify a stage convention I've ever run across. It's the only time in the play when any such realistic motivation for a ghost-darkened stage is offered. And within a very few minutes afterward we'll be seeing the dead soldier appearing in full white light to pledge allegiance to his flag, appearing in half-blue or quarter-blue mists as he pleases. One imagines that fine director, Marshall W. Mason, simply throwing up his hands and instructing the overworked folk on the lightboard to forget about lame excuses and do anything to keep Mr. Wilson's story on the move. Author Wilson himself, rather plainly, is no more certain about his dead boy's need for an other-worldly ambience than he is about the lad's corporeality.The lad's corporeality - oh, let's call it his physical solidity - comes into question because of another peculiar dramatic inconsistency. Throughout the evening the ghost, whose name turns out to be Timmy, is not seen, heard or touched by anyone else. With, once again, a single exception. Toward the end of the first half there's a great climactic rowdydow going on. The laundress's sassy daughter has been baiting the dozing Mr. Weaver, only to have him rear up roaring and crack her across the face, leaving her with a bloody nose and mouth. In retaliation, the girl announces to the family - including Mr. Higgins's wife - that Mr. Higgins is really her daddy. While the shock of this disclosure is tingling through many a nerve-end, the factory manager -who is also on the draft board - enters solemnly carrying a telegram. Yes, it is the first news the family has that Timmy is dead. Timmy hears it himself, having just slipped back in from the garden. And, as his mother reels and collapses in a dead faint, it is Timmy the ghost who rushes forward to cushion her fall, catching her in his suddenly entirely tangible arms. Exactly how it will ever be explained to the others present why mother's head never does strike the ground but remains suspended in air though quite unsupported, I can't imagine. But Timmy is as adjustable as his light-effect is; he can become mortal if it helps make a tableau.I spent some time on these curious matters because they're stylistically teasing in themselves and because they're so representative of Mr. Wilson's catch-as-catch-can play. ''A Tale Told'' is not really a tale at all but a confusing amalgam of fragments from many different tales, some of them - I'm afraid - on the familiar side. Of course the business bargaining is reminiscent of ''The Little Foxes,'' though pallidly so; echoes of Arthur Miller creep in here and there, too. The 17-year-old's finger-pointing stunner, ''I get to thinkin' it's about time for me to move up here with my daddy!,'' sounds a little like Oscar Wilde being careless at the end of Act Three in ''A Woman of No Importance,'' Missouri version. And the business of Mr. Weaver's forcing a marriage on two youngsters (bribery in exchange for blackmail) would have served well enough - did serve well enough - for many a 19th-century melodrama.Given the author and the production's auspices, there are of course fleeting good things to be grasped at. Elizabeth Sturges, as the dying Lottie, is venonmously wry about the family's failings. Mr. Weaver is admirable at every twitch, especially forceful when he's letting Mr. Higgins know that he's wiped his nose for the last time. And Sally Talley, once more in the mothlike, engaging person of Trish Hawkins, appears briefly at evening's end to pack a suitcase before running off with her victorious lover. The Circle Rep never seems to have any difficulty rounding up fine actors.The difficulty here, I think, is that playwright Wilson has no genuinely interesting people to put inside that house above the river, no new insight into the Waspish world that created them. The indoor Talleys of 1944, casually contemptuous of Roosevelt, Jews and people poorer than themselves, are thin, unfelt stereotypes; such scoundrelly tricks as they play are stock. Sally was wise to leave them. Mr. Wilson might be, too.